The present invention relates to an intake manifold for an engine, and more particularly to an intake manifold that is suitable for promoting generation of tumble flow or swirl flow in cylinders of an engine.
For example, Japanese Laid-Open Patent Publication No. 2007-113482 and Japanese Laid-Open Patent Publication No. 2008-45430 disclose such typical intake manifolds.
The intake manifold disclosed in Japanese Laid-Open Patent Publication No. 2007-113482 is made of synthetic resin and has an intake passage connected to one of intake ports of an engine. A downstream section of the intake passage is divided into upper and lower regions by a partition. A synthetic resin valve for opening and closing the lower region in the intake passage is provided in the intake passage at a position upstream of the partition. When the lower region in the intake passage is closed by the valve, flow of air that flows into one of engine cylinders from the intake manifold through the upper region in the intake passage generates tumble flow in the engine cylinder.
In the case of this intake manifold, molding distortion in the synthetic resin intake manifold and valve can cause the side edges of the valve to interfere with wall surface that defines the intake passage to such an extent that the side edges hinder the operation of the valve. To eliminate such a drawback, it is inevitable that a clearance is provided between each side edge of the valve and a portion of the intake passage wall surface that faces the side edge of the valve. Therefore, when the lower region in the intake passage is closed by the valve, air flows into one of the engine cylinders from the intake manifold not only through the upper region in the intake passage, but also through the clearances. This disadvantageously reduces the efficiency of generation of tumble flow in the corresponding engine cylinder.
The intake manifold disclosed in Japanese Laid-Open Patent Publication No. 2008-45430 is made of synthetic resin and has intake passages each connected to one of intake ports of an engine. A synthetic resin valve is arranged in each intake passage. The valves are supported at their proximal ends by a shaft. Each valve rotates integrally with the shaft to open and close the corresponding intake passage. Each valve has a slit, which is formed by cutting out a part of the distal end of the valve. When each intake passage is closed by the corresponding valve, the slit of the valve allows air to flow therethrough to one of the engine cylinders. The airflow through the slit of each valve generates tumble flow in the corresponding engine cylinder.
In the case of this intake manifold also, it is inevitable that a clearance is provided between each side edge of each valve and a portion of the corresponding intake passage wall surface that faces the side edge of the valve. Therefore, when each intake passage is closed by the corresponding valve, air flows into the engine cylinders from the intake manifold not only through the slits of the valves, but also through the clearances. This disadvantageously reduces the efficiency of generation of tumble flow in the cylinders.